Industrial robots make it possible to move an object in space, according to a certain number of degrees of freedom of the latter. Such robots provide the movement of parts, typically very heavy or too bulky to be able to be moved by a human operator, for example on production lines. Such robots can also provide the precise positioning of these parts, for example in order to carry out assembly operations. As not all of the tasks carried out by industrial robots can be fully automated, some of them require a human operator to control them. Typically, an industrial robot is a system comprising a plurality of articulations, like a human arm. It can be in the form of a manipulator arm, equipped at one end with a grasping member able to grasp the part. The part can be spatially oriented by the robot, for example in rotation about three axes, and in translation along the aforesaid three axes; in any case the combined movements of the elements constituting the robot must allow manipulation of the part, making it possible to move and orient it in space.
In order to prioritize a precise manipulation of the part, the movements of the grasping member of the robot can be constrained so that involuntary movements of the operator do not deflect the manipulated part; for example the movements applied by the robot can be constrained in translation or in rotation. In such cases, it is said that the part is moved along “virtual guides”, each forming a type of assistance to the operator. The present invention is included in the context of robots providing assistance like virtual guides.
There are various robot control systems. Notably, there are known control systems by means of which the operator can interact directly with the robot, for example by the intermediary of a control grip fixed at the level of the grasping member of the robot and allowing the operator to move the latter. In this way the part can be manipulated in its six degrees of freedom, it being possible to strictly compensate for the weight of the part. However, more particularly when the operator has to manipulate a part having large dimensions with precision, it can be difficult for him to control the robot solely by means of a control grip fixed at an end of the arm of the robot. Not only can it be essential for the operator to grasp a particular place on the part in order to be able to manipulate it in a certain way, but the fixed grip can also become out of reach to the operator when the robot has to grasp a single part having large dimensions.
In order to overcome these disadvantages, control systems have been designed allowing an operator to interact with a part to be manipulated by means of the part itself, by a control member remote from the robot and allowing a direct interaction with the part, located at an end of the part. Such a control system is described in the Japanese patent application published under the reference JP 2008/213119. In this control system, a grip remote from the robot can be disposed at a predetermined location on a frame supporting the part to be manipulated.
According to another technique, described in the patent application lodged under the reference FR 11/61402, control means can be fixed in a detachable manner by the operator at desired places on the part to be manipulated.
A disadvantage of systems in which the forces applied by the human operator are applied at a distance from the robot is related to the fact that the forces applied by the operator at the point of holding the part are different from the forces felt by the grasping member of the robot, which can involve ambiguities between different movements, for example the movements of rotation and of translation. For example, in a configuration where the operator and the grasping member of the robot grasp each end of a part, for example a board, the force felt at the level of the grasping member of the robot is like a torque, as though the operator wishes to pivot the part around the effector of the robot, even though he wishes to move it in translation. There is thus ambiguity with regard to the interpretation of the forces applied by the operator.
Solutions have been proposed to overcome these disadvantages. For example, in order to resolve a rotation/translation ambiguity, it is possible for the operator to apply a high torque about his holding point. However, by acting in such a way, the operator loses the advantage of the assistance provided by the robot because the application of a high torque forces him to apply a force on the part to be manipulated close to his holding point, but also close to the grasping member of the robot; in fact the operator must then apply a force in order to move the side of the part held by the robot in addition to the force applied in order to move his side of the part. Thus the robot becomes an additional constraint for the operator, who has to compensate for the moment of inertia generated by the length of the object to be manipulated and for the inertia of the robot.
According to more elaborate known techniques, starting with the hypothesis that the robot has no a priori knowledge of the tasks to be carried out and of the environment, the aforesaid disadvantage can be overcome by the definition of so-called “nonholonomic” constraints on the robot, making it possible to prohibit a movement of translation or a rotation of the manipulated object. Such techniques have the disadvantage of imposing tedious and non-intuitive efforts on the operator, for example a series of successive movements to impose on the part because of a prohibition of a movement of the manipulated object according to an unauthorized degree of freedom. It happens however that the fact of retaining the movement redundancies preserves the ability to allow the operator to carry out complex tasks rapidly and efficiently. Moreover, in more confined environments, the fact of preserving the holonomy of the possible movements ensures that this movement can be carried out, whatever the configuration may be, insofar as a path exists along which the part can be moved as desired. On the other hand, such a movement can be made impossible because of unauthorized movements in the context of methods involving nonholonomic constraints.
According to alternative known techniques, it has been proposed that the operator uses voice instructions in order to dictate his intentions to the robot and remove the possible ambiguities. Such techniques have the disadvantage of requiring complex voice recognition systems, which prove not to be very robust, notably in industrial environments that are often noisy. Moreover, such techniques introduce a significant delay between the making of a decision by the operator and the carrying out of the movement by the robot. Such techniques also have the disadvantage of not being universal: in fact the voice instructions must be recognized and notably given in a language recognized by the system. According to such techniques, the operator must also specify the reference system in which the instructions are given.
Thus, it is necessary for an assistance robot, notably for applications requiring the movement of bulky parts, to allow the holonomic movement of the part to be manipulated, whilst actively participating in the movements, in order that the operator does not have to apply forces that are too strong.